Astronomers witness the birth of a very distant cluster of galaxies from
the early Universe

Date:
March 30, 2023
Source:
ESO
Summary:
Astronomers have discovered a large reservoir of hot gas in the
still- forming galaxy cluster around the Spiderweb galaxy -- the
most distant detection of such hot gas yet. Galaxy clusters are
some of the largest objects known in the Universe and this result
further reveals just how early these structures begin to form.


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FULL STORY ========================================================================== Using the Atacama Large Millimeter/submillimeter Array (ALMA), of which
ESO is a partner, astronomers have discovered a large reservoir of hot
gas in the still-forming galaxy cluster around the Spiderweb galaxy --
the most distant detection of such hot gas yet. Galaxy clusters are some
of the largest objects known in the Universe and this result, published
today in Nature, further reveals just how early these structures begin
to form.


========================================================================== Galaxy clusters, as the name suggests, host a large number of galaxies
- - sometimes even thousands. They also contain a vast "intracluster
medium" (ICM) of gas that permeates the space between the galaxies
in the cluster. This gas in fact considerably outweighs the galaxies themselves. Much of the physics of galaxy clusters is well understood;
however, observations of the earliest phases of formation of the ICM
remain scarce.

Previously, the ICM had only been studied in fully-formed nearby
galaxy clusters. Detecting the ICM in distant protoclusters -- that is, still-forming galaxy clusters -- would allow astronomers to catch these clusters in the early stages of formation. A team led by Luca Di Mascolo,
first author of the study and researcher at the University of Trieste,
Italy, were keen to detect the ICM in a protocluster from the early
stages of the Universe.

Galaxy clusters are so massive that they can bring together gas that
heats up as it falls towards the cluster. "Cosmological simulations have predicted the presence of hot gas in protoclusters for over a decade,
but observational confirmations has been missing," explains Elena
Rasia, researcher at the Italian National Institute for Astrophysics
(INAF) in Trieste, Italy, and co- author of the study. "Pursuing
such key observational confirmation led us to carefully select one of
the most promising candidate protoclusters." That was the Spiderweb protocluster, located at an epoch when the Universe was only 3 billion
years old. Despite being the most intensively studied protocluster,
the presence of the ICM has remained elusive. Finding a large reservoir
of hot gas in the Spiderweb protocluster would indicate that the system
is on its way to becoming a proper, long-lasting galaxy cluster rather
than dispersing.

Di Mascolo's team detected the ICM of the Spiderweb protocluster through
what's known as the thermal Sunyaev-Zeldovich (SZ) effect. This effect
happens when light from the cosmic microwave background -- the relic
radiation from the Big Bang -- passes through the ICM. When this light interacts with the fast-moving electrons in the hot gas it gains a bit
of energy and its colour, or wavelength, changes slightly. "At the right wavelengths, the SZ effect thus appears as a shadowing effect of a galaxy cluster on the cosmic microwave background," explains Di Mascolo.

By measuring these shadows on the cosmic microwave background,
astronomers can therefore infer the existence of the hot gas, estimate
its mass and map its shape. "Thanks to its unparalleled resolution and sensitivity, ALMA is the only facility currently capable of performing
such a measurement for the distant progenitors of massive clusters,"
says Di Mascolo.

They determined that the Spiderweb protocluster contains a vast reservoir
of hot gas at a temperature of a few tens of millions of degrees Celsius.

Previously, cold gas had been detected in this protocluster, but the
mass of the hot gas found in this new study outweighs it by thousands
of times. This finding shows that the Spiderweb protocluster is indeed
expected to turn into a massive galaxy cluster in around 10 billion years, growing its mass by at least a factor of ten.

Tony Mroczkowski, co-author of the paper and researcher at ESO, explains
that "this system exhibits huge contrasts. The hot thermal component
will destroy much of the cold component as the system evolves, and we
are witnessing a delicate transition." He concludes that "it provides observational confirmation of long-standing theoretical predictions
about the formation of the largest gravitationally bound objects in
the Universe." These results help to set the groundwork for synergies
between ALMA and ESO's upcoming Extremely Large Telescope (ELT ), which
"will revolutionise the study of structures like the Spiderweb," says
Mario Nonino, a co-author of the study and researcher at the Astronomical Observatory of Trieste. The ELT and its state-of-the-art instruments,
such as HARMONI and MICADO, will be able to peer into protoclusters and
tell us about the galaxies in them in great detail.

Together with ALMA's capabilities to trace the forming ICM, this will
provide a crucial glimpse into the assembly of some of the largest
structures in the early Universe.

* RELATED_TOPICS
o Space_&_Time
# Galaxies # Stars # Cosmology # Astrophysics # Astronomy
# Big_Bang # Space_Telescopes # Space_Exploration
* RELATED_TERMS
o Globular_cluster o Spitzer_space_telescope o Dark_matter o
Galaxy o Barred_spiral_galaxy o Galaxy_formation_and_evolution
o Interstellar_medium o Andromeda_Galaxy

========================================================================== Story Source: Materials provided by ESO. Note: Content may be edited
for style and length.


========================================================================== Related Multimedia:
* The_Sunyaev-Zeldovich_effect_in_the_Spiderweb_protocluster ========================================================================== Journal Reference:
1. Luca Di Mascolo, Alexandro Saro, Tony Mroczkowski, Stefano Borgani,
Eugene Churazov, Elena Rasia, Paolo Tozzi, Helmut Dannerbauer,
Kaustuv Basu, Christopher L. Carilli, Michele Ginolfi, George Miley,
Mario Nonino, Maurilio Pannella, Laura Pentericci, Francesca
Rizzo. Forming intracluster gas in a galaxy protocluster
at a redshift of 2.16. Nature, 2023; 615 (7954): 809 DOI:
10.1038/s41586-023-05761-x ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/03/230330102341.htm

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